Which nerve injury results in bilateral vocal cord paralysis in the paramedian position?

Explanation

## Bilateral Vocal Cord Paralysis — Paramedian Position **Key Point:** Bilateral **Recurrent Laryngeal Nerve (RLN)** injury is the classic and most common cause of bilateral vocal cord paralysis in the **paramedian position**. ### Anatomical Basis The RLN innervates all intrinsic laryngeal muscles **except the cricothyroid**. The most critical muscle it supplies is the **posterior cricoarytenoid (PCA)** — the only abductor of the vocal cords. - When both RLNs are injured, the PCA (abductor) is paralyzed bilaterally. - Without abductor tone, the cords assume a **paramedian (near-midline) resting position** due to the unopposed action of the adductors (which are also paralyzed, but the elastic recoil and interarytenoid muscle tone place cords near midline). - This results in a **narrow glottic chink**, causing **inspiratory stridor** and potentially life-threatening airway obstruction requiring tracheostomy. ### Why Not Option C (Vagus above nodose ganglion)? Proximal vagal injury (above the nodose ganglion) does produce paramedian cord paralysis, but it **additionally** causes: - Palatal weakness, absent gag reflex - Pharyngeal and tongue deficits (bulbar signs) - Nasal regurgitation This is a **distinct clinical entity** from isolated bilateral RLN injury. The stem asks simply which nerve injury results in bilateral paramedian paralysis — the textbook answer for this isolated laryngeal finding is **bilateral RLN injury** (Scott-Brown's Otolaryngology; Cummings Otolaryngology). ### Comparison Table | Feature | Bilateral RLN Injury | Bilateral Vagal Injury (Proximal) | |---------|----------------------|-----------------------------------| | Cord position | **Paramedian** | Paramedian | | Airway compromise | Severe (stridor) | Severe + bulbar signs | | Isolated laryngeal deficit | Yes | No (multiple CN X branches affected) | | Most common clinical scenario | Yes | Rare (skull base/brainstem pathology) | **High-Yield:** Bilateral RLN injury → bilateral paramedian cord paralysis → inspiratory stridor → tracheostomy. This is the standard teaching in all ENT textbooks (Scott-Brown, Cummings, Dhingra). **Clinical Pearl:** Causes of bilateral RLN injury include thyroid surgery, neck dissection, mediastinal tumors, and aortic arch aneurysm. Always distinguish from proximal vagal lesions by checking for associated palatal/pharyngeal deficits.